From the Guidelines
Magnesium sulfate is a recommended treatment for torsades de pointes, particularly in patients with acquired QT prolongation, as it can help suppress the arrhythmia 1.
Key Points
- Intravenous magnesium sulfate is recommended for patients with QT prolongation due to medication, hypokalemia, hypomagnesemia, or other acquired factors and recurrent torsades de pointes 1.
- Potassium repletion to 4.0 mmol per L or more and magnesium repletion to normal values (e.g., ≥2.0 mmol/L) are beneficial for patients with torsades de pointes associated with acquired QT prolongation 1.
- Dosing: 1 to 2 g of magnesium sulfate intravenously, with repeated doses as needed to suppress ectopy and nonsustained VT episodes 1.
- Mechanism: Magnesium can suppress episodes of torsades de pointes without necessarily shortening the QT interval, even when serum magnesium is normal 1.
Important Considerations
- Magnesium toxicity can occur at high serum concentrations, but the risk is small with the usual doses used to treat torsades de pointes 1.
- Temporary pacing or isoproterenol may be needed in some cases, particularly if torsades de pointes is recurrent despite magnesium and potassium supplementation 1.
The FDA Drug Labels for magnesium sulfate (IV) do not address this question.
From the Research
Mechanism of Action
- Magnesium sulfate treats torsades de pointes by a direct antagonism of Mg++-K+ and/or Mg++-Ca++ 2
- It increases the ventricular effective refractory period (ERP) without changing the QT interval, resulting in a significant increase in ERP/QT 3
- Magnesium sulfate decreases the dispersion of ERP (dERP), although not significantly 3
Efficacy
- Intravenous magnesium sulfate is extremely effective in treating torsades de pointes, with a success rate of 80-100% in various studies 4, 5, 6
- It is considered the treatment of choice for torsades de pointes due to its simplicity, rapidity of administration, and almost immediate efficacy 4, 2
- Magnesium sulfate is safe to use, even in patients with acute myocardial infarction, angina pectoris, or systemic hypertension, where other treatments like isoproterenol may be contraindicated 5